Effect of lattice distortion and grain size on the crack tip behaviour in Co-Cr-Cu-Fe-Ni under mode-I and mode-II loading

Abstract

In this article, molecular dynamics (MD) based simulations were performed to study the crack tip behaviour in single and polycrystalline configurations of five elemental (Co-Cr-Cu-Fe-Ni) high entropy alloys. To investigate the crack tip behaviour in polycrystalline HEA, inter and intragranular crack positions in conjunction with grain size in the range of ∼2.5 nm to ∼10 nm were developed and simulated in this work. Average atom (A-atom) configuration was also developed to nullify the effect of lattice distortion, and results were compared with random alloy configuration/HEA. Simulations revealed that A-atom possesses higher critical stress values. Still, the early onset of dislocation emissions from the crack tip in random alloys leads to crack tip blunting. The spatial positioning of the crack in the polycrystalline HEA significantly affects the fracture behaviour. It was concluded from the simulations that in small grain size configurations (5 nm and 6 nm), crack tip was in proximity of the high energy atoms of grain boundary, which led to hardening and higher stresses at the crack tip. The higher value of crack tip stresses in small grain configurations leads to crack propagation. In contrast, early emission of dislocations from the crack tip in large grains dilutes the crack tip stresses.